Compact reforming reactor

ABSTRACT

Reforming reactor for the conversion of a process fluid into hydrogen comprising: a reforming section and a boiler section which are both contained within a common volume and a combustion section, in which said reforming section contains one or more catalyst tubes filled with reforming catalyst, said boiler section is provided with one or more tubes carrying flue gas from the combustion section and said combustion section is provided with at least one burner, wherein the heat exchanging medium required for the reforming of said process fluid in the one or more catalyst tubes is a gas-liquid mixture that self-circulates and is encapsulated inside said common volume containing said reforming and boiler sections.

FIELD OF THE INVENTION

This invention relates to an integrated and compact reforming reactorfor the production of hydrogen to be used in industrial applicationssuch as in the metallurgical industry, chemical and pharmaceuticalindustry and fuel cell power plants. In particular the invention relatesto a compact reforming reactor for the conversion of hydrocarbonfeedstocks to hydrogen where the reformed gas of the reactor is furtherenriched in hydrogen by passage through a Pressure Adsorption Swing(PSA) unit, a Pd-alloy membrane, water-gas shift unit or by PreferentialOxidation (PROX). More particularly the invention relates to a compactreforming reactor for the conversion of methanol to a hydrogen gassuitable for use in fuel cell plants, especially where the reformed gasof the reactor is further enriched in hydrogen by passage through a PSAunit. The invention further involves a process for reforming thehydrocarbon feedstock into a hydrogen gas using this reactor.

BACKGROUND OF THE INVENTION

Fuel cell plants require often the supply of hydrogen as fuel source andaccordingly a reforming reactor is normally integrated in fuel cellplants. The reforming reactor converts a suitable hydrocarbon feedstockacting as energy carrier, such as methane, liquid petroleum gas,gasoline, diesel or methanol, into a hydrogen rich gas, which then maybe passed through a hydrogen-enrichment unit before entering a fuel cellassembly. Compact fuel cell power plants may today provide about 20 kWof power and even more, for instance up to 50 kW, thereby promoting awide range of applications. One such application is the use of compactfuel cell plants in the automotive industry.

For widespread application, methanol is still regarded as the besthydrocarbon feedstock for the production of hydrogen-rich gas not onlyin connection with fuel cell plants but also for application in smallplants in other industrial fields. Roughly, methanol is particularlysuitable where the demand for hydrogen is the range 50-500 Nm³/h, whichis typical for small plants. For a hydrogen demand of above 500 Nm³/h ahydrocarbon feedstock such as natural gas is often more expedient. Below50 Nm³/h electrolysis or bottled hydrogen is normally more expedient.

Reactors for the reforming of fuel gases, particularly methanol, andwhich are used in fuel cell plants are known in the art. Dusterwald etal. disclose in Chem. Eng. Technol. 20 (1997) 617-623 a methanol steamreformer consisting of four reactor tubes that are individuallybalanced. Each reactor tube consists of two stainless tubes arrangedconcentrically with catalyst filling the inner tube and in which theheat needed for the endothermic reaction of a methanol-water mixture isprovided by condensing steam that flows in the gap between the tubes. Itis also known from U.S. Pat. No. 4,861,347 to oxidise a raw fuel such asmethanol in order to obtain an exothermic reaction, whereby the heatgenerated by this reaction is used for the endothermic reformingreaction of the hydrocarbon feedstock, which is normally a mixture ofmethanol and water. The heat is transferred from the combustion sectionof the reactor to its reforming section by means of heat tubes throughwhich a hot flue gas from the combustion section is passed or as inJP-A-63248702 by means of heat pipes arranged in the reactor. As aresult, the heat generated in the combustion system can be evenlydistributed to the rest of the reactor, whereby a uniform temperaturedistribution is obtained.

Often the heat transfer system in the reforming reactor is not rapidenough to achieve the desired operating temperature after changes inprocess conditions such as after sudden load changes or during start-upsand shut-downs, especially when separate heat pipes are provided in thereforming reactor. Normally a number of more or less sequential stepsare required for the start-up of the reforming reactor resulting in aprocedure that may be significantly tedious and time-consuming.

In the particular field of fuel cells, the advent of fuel cells withincreased power, for instance of up to 20 kW or even more, for instanceup to 50 kW has resulted in a need for providing a plurality of catalysttubes in a single reforming reactor. This in turn imposes more demandsin reactor design in terms of i.a. compactness, better temperaturedistribution and thermal efficiency. In particular, the provision of auniform temperature distribution by which all catalyst tubes inside thereactor are heated to the same temperature becomes more difficult toachieve when the heating required in reforming has to be provided bymeans of a single burner in the reactor.

In addition, the catalyst within the catalyst tubes may often be notevenly distributed so that the catalyst may for instance be betterpacked in some tubes than others. This may create undesired variation intemperature conditions across the catalyst tubes.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a reformingreactor with improved temperature distribution across all catalysttubes.

It is also an object of the invention to provide a reforming reactorwhich is compact and free for mechanical means for circulating a heatexchanging medium from the high temperature section of the reactor tothe reforming section of the reactor.

It is a further object of the invention to provide a reforming reactorwhich is compact whilst at the same time is able to rapidly and simplyachieve or maintain its operating temperature after a change in processconditions, such as a change in hydrocarbon feed flow or temperature ora change in burner conditions or during a start-up operation.

It is another object of the invention to provide a reforming reactorwhich is less sensitive to divergent catalyst packing across thecatalyst tubes.

It is another object of the invention to provide a reforming reactorwhich is simple in its construction, inexpensive and with lower heatloss than in conventional reforming reactors.

It is yet another object of the invention to provide a reforming reactorwhich is compact and suitable for use in fuel cell plants, particularlyfor fuel cell plants capable of producing up to 20 kW of power or evenmore for instance up to 50 kW.

These and other objects are achieved by the reactor and process of theinvention.

In a first aspect of the invention we provide a reforming reactor forthe conversion of a process fluid into hydrogen comprising: a reformingsection and a boiler section which are both contained within a commonvolume and a combustion section, in which said reforming sectioncontains one or more catalyst tubes filled with reforming catalyst, saidboiler section is provided with one or more tubes carrying flue gas fromthe combustion section and said combustion section is provided with atleast one burner, wherein the heat exchanging medium required for thereforming of said process fluid in the one or more catalyst tubes is agas-liquid mixture that self-circulates and is encapsulated inside saidcommon volume containing said reforming and boiler sections.

Accordingly, in the invention a gas-liquid mixture circulating outsidethe catalyst tubes in the reforming section and outside the tubescarrying the flue gas in the boiler section provides for a large heatsink that enables the accumulation and supply of heat for the reformingreaction so that all metal parts within the reactor, particularly thecatalyst tubes, maintain or rapidly reach the same temperature, and arobust operation of the reactor is obtained as it becomes i.a. lesssensitive to temporary changes in process conditions, such as changes inburner duty.

By the term “self-circulates” it is meant that the gas-liquid mixtureacting as heat exchanging medium moves internally in the reactor withoutthe need of any mechanical means. The gas flows to surfaces or catalysttube walls, where condensation takes place in a movement driven by theslightly lower pressure created by the volume reduction of the gas as ittransforms into liquid. Liquid flows then to the boiler section drivenby gravity forces.

In the reactor of the invention at least one process feed tube carryingthe process fluid to be converted, such as a liquid mixture of methanoland water, may extend inside said common volume of the reactor.Accordingly, the at least one process feed tube may extend into anylocation inside said common volume containing the reforming and boilersection, for example the at least one process feed tube may extend froma region at the top of the reactor and above the reforming section intothis reforming section or even further into the boiler section arrangedbelow. The at least one process feed tube carrying the process fluid tobe converted is introduced to the reactor through a conduct in the outerwall of the reactor and may then extend into the reactor from saidconduct arranged in the outer wall. Preferably said process feed tubeextends substantially co-axially of the reactor wall inside said commonvolume from the reforming section of the reactor to the boiler sectionof the reactor. This enables the provision of a compact reactor as theat least one process feed tube, for example a single substantiallystraight tube or a tube bundle, is advantageously integrated within thereactor whereby the preheating or evaporation of the process fluid canadvantageously be effected as the gas in the self-circulating gas-liquidmixture outside the tube condenses. Hence it is possible to integratethe required evaporation stage inside the reactor thus avoiding theinexpedient provision of separate evaporation means outside the reactor.

By the term “extends substantially co-axially” it is meant that aportion of the process feed tube, particularly the inlet portioncooperating with the conduct in the outer wall of the reactor, mayextend into the center of the reactor in a direction which isperpendicular to the reactor length axis, thereafter bending 90° andconsequently extending vertically into the reforming section or boilersection below.

The at least one process feed tube may extend vertically into atransition compartment from which at least one process tube carryingprocess gas to be converted extends vertically upwards inside the commonvolume of the reactor and wherein the at least one process tube carryingthe process gas is formed as a coil. Preferably, a single process tubedescends from the conduct in the outer wall where the hydrocarbon feedfor example a liquid hydrocarbon feed enters the reactor to thetransition compartment. The transition compartment is arranged as a boxhaving inlet openings adapted to accommodate the at least one processtube carrying a process fluid present in substantially liquid form andoutlet openings adapted to accommodate the at least one process tubecarrying a process fluid present in substantially gas form. These tubesextend vertically upwards and are formed as a coil or spiral. Thisensures a better heat transfer for the preheating of the process gasprior to reforming and provides at the same time a compact reactordesign as the same heat transfer area as for instance a straight tubecan be accommodated in a lower height. Furthermore, the use of a coil orspiral imparts a centrifugal effect on the two-phase flow (gas-liquid)thereby enabling backflow of any liquid not yet evaporated andfacilitating the upward flow of process gas.

Preferably the at least one process tube extends from a transitioncompartment in the boiler section of the reactor to the reformingsection in order to ensure that the process gas is heated to the properreaction temperature in the reforming section.

In the invention it is also possible to extend the at least one processfeed tube into a transition compartment located in the combustionsection for example in a flue gas region just underneath the boilersection.

In this specification the term “hydrocarbon feedstock” is usedinterchangeably with the term “process fluid” or “feed process fluid”.Normally, the feed inlet to the reactor, for example a mixture ofmethanol and water is present in liquid form whereas when entering intothe reforming section it is present in gas form. When entering thereactor, the hydrocarbon feed is also referred as process fluid andafter evaporation in the process tube the resulting fluid is alsoreferred as process gas. The term “process feed tube” as used hereinrefers to the at least one tube carrying the process fluid and whichenters the transition compartment. The tubes protruding from thetransition compartment and carrying the evaporating gas that is directedto the reforming section are referred simply as “process tubes”.

In another embodiment of the invention the at least one process feedtube carrying the process fluid to be converted enters the reactorthrough a conduct arranged in the outer wall of the reactor and saidprocess fluid is preheated by indirect contact (i.e. across a heattransfer surface) with exiting converted gas from the reforming sectionof the reactor, in which said exiting converted gas preferably passes inthe annular region of said conduct. Normally the PSA unit downstreamrequires a relatively cold stream of hydrogen-rich gas and accordinglycooling means such as an air cooler downstream the reactor is used.Hence, this embodiment enables the reformed gas from the reactor(hydrogen-rich gas) to be cooled from normally about 280° C., which istypical for the reforming of methanol to about 150° C., thereby reducingthe effect required in the air cooler downstream and accordingly alsoreducing its size. The portion of the at least one process tube carryingthe process fluid which is in contact with the exiting converted gasfrom the reforming section may advantageously be formed as a coil toensure an even more compact reactor design without too noticeableprotruding parts. Said conduct is preferably located in the upperportion of the reactor, e.g. near its top. In an alternative embodiment,an outlet tube carries the exiting converted gas and runs parallel withthe process feed tube inside said conduct.

In the combustion section arranged preferably in the lower portion ofthe reactor and below the boiler section, a suitable fuel, such asmethanol is injected through a fuel inlet and is subjected to a reactionwith preheated combustion air in the at least one burner. Hot flue gasesare produced by the exothermic oxidation of methanol and are then passedto the boiler section. The tubes carrying said flue gases may extendvertically from the combustion section into the boiler section and theiroutlets may then protrude from said boiler section towards an annularsection of the reactor.

The boiler section is contained within a compartment or common volume inwhich a gas-liquid system, preferably a saturated gas-liquid mixture,such as a saturated water-steam mixture, self-circulates. Thecompartment contains one or more tubes through which hot flue gas from acombustion section arranged below passes. The hot flue gas supplies heatto the gas-liquid mixture thereby evaporating part of the liquid andpromoting its circulation upwards internally in the reactor. Part of theheat in the gas-liquid mixture is also delivered to the at least oneprocess tube carrying the gas or liquid or gas-liquid mixture to beconverted, e.g. methanol-water. The process tubes extend away from theboiler section and upwardly through the middle portion of the reactorand further up to the reforming section inside which one or morevertical catalyst tubes are disposed. The reforming section is alsocontained within the same compartment or common volume as the boilersection, but is preferably arranged separately in the upper portion ofthe reactor. Hence, said boiler and reforming section are both containedwithin a common volume. The term catalyst tube means that these tubesare filled with solid catalyst particles suitable for the reforming of agiven hydrocarbon feedstock, such as a mixture of methanol and water.

Prior to reforming, the process gas to be reformed leaves the processtubes at a suitable position in the reformer section, preferably abovethe one or more catalyst tubes. The one or more catalyst tubes arenormally arranged as a plurality of circumferentially and radiallyspaced catalyst tubes. Often the number of catalyst tubes is over 5 or20, more often over 50 and even above 100 or 200 depending on thehydrogen capacity of the reactor. The process gas to be reformed entersthe catalyst tubes and flows downwards through the catalyst particles soas to be gradually converted along its passage through the catalysttubes. The heat required for the reforming reaction is provided by thegas-liquid mixture which self-circulates outside said catalyst tubes. Asthe gas-liquid mixture delivers heat to the catalyst tubes, the gascondenses and via gravity is forced to flow downwards to the boilersection. The gas-liquid mixture acting as heat exchanging medium movestherefore inside the reactor in a self-circulating manner in a regionwhich is encapsulated inside said common volume containing the boilersection and the reforming section. This enables the continuouscirculation of the gas-liquid mixture through said boiler section andsaid reforming section inside the reactor.

It would therefore be understood that the gas-liquid mixtureself-circulates outside the at least one process feed tube, outside theat least one process tube carrying the process gas to be converted,outside the tubes carrying the flue gas, and outside the one or morecatalyst tubes in a hermetically sealed compartment. The gas or liquidin the mixture, for instance steam when the mixture is a saturatedwater-steam mixture, is not utilised for other purposes other than asheat transfer medium as described above.

Preferably at least said reforming and boiler sections are arrangedco-axially in the reactor so as to be able to fit into an outersubstantially cylindrical housing. Accordingly, in one embodiment saidcombustion, reforming and boiler sections are arranged co-axially in thereactor. In another embodiment the reforming and boiler section may bearranged co-axially in the reactor, while the combustion section may bearranged normal to said boiler section so as to form an L-shapedreactor. This enables a lower length in the reactor and may facilitateits transport under circumstances where reactor length is a limitingfactor.

Said reforming section is preferably arranged in series with respect tothe boiler section in which the at least one process tube carrying theprocess gas and optionally the at least one process feed tube carryingthe process fluid inlet are disposed co-axially. The boiler section ispreferably arranged in series with respect to a combustion section,which apart from the one or more burners may also comprise a fuel inletfor the introduction of a suitable fuel, preferably methanol, andoptionally a co-axially arranged fuel inlet for the introduction ofanother fuel, which is preferably off-gas from the PSA unit or any otheroff-gas from a hydrogen enrichment step. Typically during normaloperation of the reactor, the off-gas from the PSA serves as main fuel,whereas methanol serves as supporting fuel, whereas upon a start-up itis methanol that serves as the main fuel. The use of off-gas from thePSA unit and optionally the anode off-gas from the fuel cell enablesbetter overall thermal efficiency in for instance a fuel cell plantcomprising said reactor and said accompanying PSA unit.

The combustion section of the reactor is also provided with at least oneburner. Because of the requirement of reactor compactness the number ofburners is kept at a minimum. Preferably a single burner is provided;more preferably a single catalytic burner is provided. The catalyticburner may be a ceramic hollow cylinder with oxidation catalyst on itsouter surface to which fuel gas premixed with air is suppliedinternally. The catalytic burner is preferably a burner arranged in aflow channel and provided as wire mesh layers arranged in series whichare coated with ceramic and impregnated with an oxidation catalyst. Theheat generated in the combustion is transferred by a convectionmechanism to the self-circulating gas-liquid system via the generatedflue gas. Accordingly, in another embodiment of the invention, in thereactor said combustion section is provided with a single catalyticburner and wherein said catalytic burner is provided as wire mesh layersarranged in series which are coated with ceramic and impregnated with anoxidation catalyst, whereby the heat generated in the combustion istransferred by a convection mechanism to the self-circulating gas-liquidmixture via the generated flue gas. This enables a better transfer ofheat than in for instance systems in which heat transfer occurs by aradiation mechanism, while at the same time enables a compact reactordesign since only a single burner is used.

In another embodiment of the invention said reforming section and boilersection are substantially surrounded by an insulated housing, whereinsaid insulated housing is encased by a first annular region carryingflue gas and a second annular region carrying combustion air. Thisenables a low heat loss to the surroundings since the hotter partswithin the main body of the reactor containing the reforming section,combustion section and the common volume carrying the gas-liquid systemserving as heat exchanging medium is encased by first an insulatedhousing, then a sleeve through which flue gas is passed and finally asecond (outer) annular region carrying combustion air to be used in theburner. This may also enable that combustion gas and any other suitablefuel gas, such as off-gas from a hydrogen-purification unit downstream,be preheated by indirect heat exchange with the flue gas, whichpreferably runs counter-currently on its way out of the reactor. In apreferred embodiment, the flue gas enters into said first annular regiondirectly from the boiler section via an annular region outside saidboiler section. This annular region is fed with flue gas by means oftubes carrying this gas that protrude from the boiler section. The fluegas may also enter into said first annular region directly from thecombustion section of the reactor, whereby a higher temperature in theflue gas may be effected.

By the term “substantially surrounded by an insulated housing” as usedherein is meant that some portions of the reactor may not be insulated.For instance it is possible that part of the reforming section does notrequire insulation. It is also possible that a small portion of thereforming or boiler section is not surrounded by said insulated housing.For instance, the insulated housing may not cover the lower portion ofthe boiler section closest to the combustion section.

The reactor may be adapted to cooperate with a Pressure Swing Adsorptionunit (PSA), which is the preferred hydrogen-purification unit for thefurther treatment of the reformed process gas leaving the reactor. Asmentioned above, the off-gas from the PSA unit may be utilised in thereactor as fuel. Hence, in yet another embodiment of the invention aninlet is adapted to said second annular region carrying combustion airfor the passage of PSA off-gas. This enables the preheating of saidoff-gas prior to introduction into the at least one burner in thecombustion section.

Instead of a PSA-unit a Pd-alloy membrane may also be used to enrich thereformed process gas. Normally a higher degree of purity may be obtainedby using Pd-alloy membranes which may be incorporated into the reactor.Accordingly, in the invention it is also possible that a hydrogenpurification unit, such as a Pd-alloy membrane is integrated within thereactor. However, a PSA purification unit is still preferred as it isless sensitive and more inexpensive than Pd-alloy membranes. Normally aPd-alloy membrane requires also a relatively high temperature in thereformed gas for instance about 350° C. Hence, in methanol reforming thereformed gas leaving the reactor at about 300° C. will require heatingin order to conform to the requirements of a Pd-alloy membrane. Otherhydrogen enrichment units such as conventional water-gas shift step,e.g. low shift and the selective oxidation of carbon monoxide in what isalso referred as Preferential Oxidation (PROX) of carbon monoxide, mayadvantageously be used particularly in connection with fuel cells. Thewater-gas shift and PROX steps enable the removal of carbon monoxidefrom the reformed hydrogen-rich gas. This results in an increase in theefficiency of electrochemical reactions in proton exchange membrane(PEM) fuel cells, since carbon monoxide adsorbed in the Pt anode of thePEM fuel cell inhibits the dissociation of hydrogen to protons andelectrons and consequently strongly reduces the power output orperformance of the PEM fuel cell.

The second annular region of the reactor carrying the combustion air ispreferably connected to the combustion section. Accordingly, said secondannular region may preferably extend into the combustion section inorder to ensure that the preheated combustion air enters into the burnertogether with the inlet fuel, which preferably is methanol and the otherfuel, which preferably is off-gas from the PSA unit. It would beunderstood that instead of air, any other suitable oxidant, such asoxygen enriched air, may be used.

The gas-liquid mixture is preferably a saturated steam-water system thatself-circulates at a pressure of about 55 to 110 bar g, preferably 65 to110 bar g and a temperature of 270° C. to about 320° C., preferably 280°C. to about 320° C. Most preferably the saturated steam-water systemself-circulates at a pressure of 65 bar g and a temperature of 280° C.It would be understood that the temperature is determined by thesaturated steam pressure in the circulating system, in this case 280° C.where the pressure of the saturated steam-water system is 65 bar g.Accordingly, the saturated steam-water system may also self-circulate ata pressure of 110 bar g and a temperature of about 320° C., or at apressure of 55 bar g with a temperature of 270° C. The saturatedsteam-water system enables the provision of a self-circulating system inwhich the temperature required in the reforming section for theconversion of methanol to hydrogen, for example 280° C., is easilyachieved. The above pressures and temperatures are particularly suitablewhen the process gas to be reformed comprises methanol, for example amixture of methanol and water, since the reforming of methanol normallyoccurs in the temperature range of 250-350° C. Accordingly, in anotherembodiment of the invention the process fluid entering the reactor is amixture of methanol and water and the gas-liquid mixture is a saturatedsteam-water system circulating at a pressure of 55 to 110 bar g and atemperature of 270° C. to about 320° C. (more specifically 318° C.). Thehigh heat capacity of the saturated steam-water system enables thereforethe provision of a large heat sink in the reactor. Heat is accumulatedand ready to be used when the circumstances, e.g. changes in reactoroperation or burner duty, so require it. Heat is distributed throughoutthe reactor by the self-circulating steam-water system, in which wateris vaporized by heat exchange with hot flue gas from the catalyticburner, while steam condenses where heat is consumed.

On the process fluid side, the pressure is kept at a lower level,normally in the range of 3 to 30 bar g, such as 20 to 30 bar g. Forinstance the pressure of the process fluid entering the reactor, here aliquid mixture of methanol and water, may be about 22 bar g and itstemperature in the range 0° C. to 50° C., while in the reformed gasleaving the reactor the pressure may be slightly lower, for example 20bar g and the temperature in the range 120° C. to 270° C. The hydrogenproduction from the reactor (exiting reformed gas) is normally in therange 10-5000 Nm³/h, often 15-1000 Nm³/h, preferably 25-1000 Nm³/h, morepreferably 25-500 Nm³/h. Normally the composition of said reformed gasis about 65% vol. H₂, 11% vol. H₂O, 2.1% vol. CO, 23% vol.CO₂ and 1.4%vol. methanol. The methanol conversion in the reactor is normally above90%, often above 95%, for example 97 to 99%. For a reactor having ahydrogen capacity (production) of 600 Nm³/h the number of catalyst tubesis normally in the range 110-120. The catalyst tubes are normally 2.5 to3.0 m long and with internal diameter of 20 mm. The temperature in thereactor across the catalyst tubes in the reforming section is kept at auniform level, for instance at 280° C., and this level is determined bythe saturated steam pressure in the circulating system, in this case 65bar g. For higher temperature applications, the self-circulating systemmay comprise sodium or potassium instead of a water-steam mixture.

The reactor may further comprise a fixed bed of catalyst arranged abovesaid catalyst tubes, in which said fixed bed covers substantially thewhole horizontal cross section of the reactor and wherein said fixed bedis adapted to receive the process gas to be converted prior to thepassage of said gas into said catalyst tubes. The fixed bed of catalystmay surround the one or more process tubes carrying the process gas tobe converted. Accordingly, the fixed bed is arranged upstream the one ormore catalyst tubes of the reforming section. The one or more processtubes carrying the process gas extends through the fixed bed and mayprotrude slightly away from the bed. The process tubes may thus beprovided with an outlet opening right above the fixed bed to allow thepassage of process gas through said bed and subsequently through thecatalyst beds inside the one or more catalyst tubes. The fixed bed ofcatalyst covering substantially whole horizontal cross section of thereactor serves as a poison guard catalyst layer and enables often thatthe process gas flows into the catalyst tubes downstream evenly andconsequently better temperature distribution across the horizontal crosssection of the reactor is achieved.

It would be understood that the integrated and compact reactor accordingto the invention integrates in a single unit a number of process unitsor steps which may otherwise require stand-alone operation outside thereactor, such as heaters for the preheating and evaporation of thehydrocarbon feedstock, preheating of combustion air and optionallypreheating off-gas from a PSA unit, as well as catalytic burners and thecommon volume encapsulating said gas-liquid mixture (gas-liquid system)serving as heat exchanging medium. The reactor does not require the useof moving parts such as valves and pumps, for instance it is notnecessary to have a pump to provide for the internal circulation of thegas-liquid mixture serving as heat exchanging medium inside the reactor.

In a second aspect the invention encompasses also a process for theproduction of hydrogen. Accordingly, we provide a process for theproduction of hydrogen from a feed process fluid in a reactor containinga combustion section, a boiler section and a reforming section asdescribed herein, the process comprising:

-   -   optionally preheating a feed process fluid by indirect heat        exchange with exiting reformed process gas from said reforming        section,    -   optionally further heating and evaporating said feed process        fluid in the reactor to form a preheated process gas by indirect        heat exchange with a gas-liquid mixture that self-circulates and        is encapsulated inside a common volume containing said reforming        section and said boiler section,    -   passing a preheated process gas through said reforming section,    -   heating the at least one catalyst tube in the reforming section        by indirect heat exchange with a gas-liquid mixture that        self-circulates and is encapsulated inside a common volume        containing said reforming section and said boiler section,    -   retrieving reformed process gas from said reforming section and        optionally cooling said reformed process gas by preheating of        the feed process fluid,    -   introducing a fuel into the at least one burner in the        combustion section together with combustion air, in which said        combustion air is preheated by indirect heat exchange with flue        gas from the boiler section,    -   retrieving flue gas from the burner and passing said flue gas        through a boiler section, and    -   heating said gas-liquid mixture that self-circulates and is        encapsulated inside a common volume in the reactor containing        said reforming section and said boiler section by indirect heat        exchange with the flue gas passing through said boiler section.

The process enables the production of reformed process gas which is richin hydrogen and which is particularly suitable for use in PSA-units.Alternatively, where a Pd-alloy membrane or similar is used ashydrogen-purification unit instead of a PSA, further heating of thereformed process gas may advantageously be effected by means of indirectheat exchange with flue gas. The hydrogen-purification unit may thus bea membrane which may also be integrated within the reactor.

The fuel introduced into the at least one burner in the combustionsection together with combustion air may be a hydrocarbon fuel, such asmethanol, but is often only off-gas from a PSA-unit downstream used ashydrogen-enrichment unit.

The above process may further comprise the steps of:

-   -   passing the cooled reformed process gas through an air cooler,    -   subsequently passing said cooled reformed process gas through a        hydrogen-purification unit to form a hydrogen-enriched gas, and    -   introducing off-gas from said hydrogen-purification unit into        the at least one burner of the reactor.

Where the hydrogen-purification unit is a PSA-unit, this unit and theair cooler are preferably located outside the reactor. The off-gas fromthe PSA unit may then be introduced into the at least one burner, asdescribed above. The hydrogen-enriched gas from thehydrogen-purification unit may then be used for any suitable industrialapplication, such as in the metallurgical industry, electronics,chemical and pharmaceutical industry or as hydrogen source in fuel cellplants.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further illustrated by the accompanying drawing inwhich the sole FIGURE shows a schematic of the reactor according to oneembodiment of the invention for production of 25-1000 Nm³/h of hydrogenfor use with a PSA-unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1 a cylindrical integrated reactor 1 with capacity of 80 Nm³/hof hydrogen contains a combustion section 2, boiler section 3 andreforming section 4. The cylindrical reactor 1 has a total weight of 300kg and is about 1.6 m high, with a diameter (except for the combustionsection) of about 0.4 m. The total volume of the reactor is about 0.275m³ while the total catalyst volume is 0.020 m³.

The reforming section 4 encompasses also a fixed bed of reformingcatalyst 5 arranged above the region of the reforming section in whichcatalyst tubes are disposed. These sections are arranged co-axially inthe reactor so as to be able to fit into an outer substantiallycylindrical housing.

A mixture of methanol and water is introduced to reactor 1 through aconduct 6 in the outer wall of the reactor. Through the conduct 6 runs aprocess feed tube 7 carrying the process fluid (methanol and watermixture). The process tube extends vertically downward to boiler section3.

The boiler section is arranged in a compartment or common volume 8inside which a saturated water-steam mixture 9 self-circulates hereillustrated by the hatched region. The saturated water-steam mixturemoves therefore inside the reactor in a self-circulating manner in aregion which is encapsulated inside said common volume 8 containing theboiler section and the reforming section. The compartment or commonvolume 8 contains one or more tubes 10 through which hot flue gas 11from the combustion section 2 arranged below passes. In combustionsection 2 arranged in the lower portion of the reactor below the boilersection 3, a suitable fuel such as methanol is injected through fuelinlet 12 which is adapted as a spray nozzle. Methanol is then subjectedto a reaction with preheated combustion air entering via inlet 13 in asingle catalytic burner 14 comprising wire meshes impregnated withoxidation catalyst and which is disposed in a flow channel co-axially ofthe cylindrical reactor 1. Hot flue gases 11 are produced and are thenpassed to boiler section 3. The tubes 10 carrying said flue gases extendvertically from combustion section 2 into boiler section 3 and theiroutlets 15 protrude towards an annular section 16 of the reactor.

In boiler section 3 within common volume 8 part of the heat in thesaturated water-steam mixture 9 is delivered to a system of processtubes 17. The process tubes 17, here formed as a coil or spiral extendaway from a transition compartment 18 in boiler section 3 and upwardlythrough the middle portion of the reactor and further up to thereforming section 4. The reforming section 4 inside which one or morevertical catalyst tubes 19 are disposed is arranged in the compartmentor common volume 8 in the upper portion of the reactor. The process gasto be reformed travelling inside process tubes 17 leaves above the fixedbed of catalyst 5 passes through this bed and enters the catalyst tubes19. The reformed gas leaves the reforming section through outlet pipe 20at the bottom of the catalyst tubes 19 and is used to preheat thehydrocarbon feed being transported inside process feed tube 7 in conduct6 at the outer wall of the reactor.

The reforming section 4, 5 and boiler section 3 are surrounded by aninsulated housing 21. This insulated casing 21 is encased by a firstannular region 22 carrying flue gas and a second annular region 23carrying combustion air which enters via inlet 13. The combustion air ispreheated by indirect heat exchange with the flue gas 11 runningcounter-currently in annular section 22 towards the flue gas exit 24.The combustion section 2 is also surrounded by a separate insulatedhousing 25. Off-gas from a PSA-unit downstream is also used as fuel andenters via inlet 26 to the burner 14. The flue gas 11 enters into saidfirst annular region 22 directly from the boiler section via an annularregion 27 outside said boiler section. The second annular region 23carrying the combustion air is connected to the combustion section 2 vianarrow passageway 28.

1. Reforming reactor for the conversion of a process fluid into hydrogencomprising: a reforming section and a boiler section which are bothcontained within a common volume and a combustion section, in which saidreforming section contains one or more catalyst tubes filled withreforming catalyst, said boiler section is provided with one or moretubes carrying flue gas from the combustion section and said combustionsection is provided with at least one burner, wherein the heatexchanging medium required for the reforming of said process fluid inthe one or more catalyst tubes is a gas-liquid mixture thatself-circulates and is encapsulated inside said common volume containingsaid reforming and boiler sections.
 2. Reactor according to claim 1, inwhich at least one process feed tube carrying the process fluid to beconverted extends inside said common volume of the reactor.
 3. Reactoraccording to claim 2, in which the at least one process feed tubecarrying the process fluid to be converted enters the reactor through aconduct arranged in the outer wall of the reactor and wherein saidprocess fluid is preheated by indirect contact with exiting convertedgas from the reforming section of the reactor.
 4. Reactor according toclaim 2, in which said at least one process feed tube extends verticallyinto a transition compartment from which at least one process tubecarrying process gas to be converted extends vertically inside thecommon volume of the reactor and wherein the at least one process tubecarrying the process gas is formed as a coil.
 5. Reactor according toclaim 1 in which said common volume containing said reforming sectionand boiler section are substantially surrounded by an insulated housing,wherein said insulated housing is encased by a first annular regioncarrying flue gas and a second annular region carrying combustion air.6. Reactor according to claim 1, wherein the process fluid entering thereactor is a mixture of methanol and water and the gas-liquid mixture isa saturated steam-water system circulating at a pressure of 55 to 110bar g and a temperature of 270° C. to about 320° C.
 7. Reactor accordingto claim 1, wherein said combustion section is provided with a singlecatalytic burner and wherein said catalytic burner is provided as wiremesh layers arranged in series which are coated with ceramic andimpregnated with an oxidation catalyst, whereby the heat generated inthe combustion is transferred by a convection mechanism to theself-circulating gas-liquid mixture via the generated flue gas. 8.Reactor according to claim 1, further comprising a fixed bed of catalystarranged above said catalyst tubes, in which said fixed bed coverssubstantially the whole horizontal cross section of the reactor andwherein said fixed bed is adapted to receive the process gas to beconverted prior to the passage of said gas into said catalyst tubes. 9.Process for the production of hydrogen from a feed process fluid in areactor containing a combustion section, a boiler section and areforming section according to any preceding claim, the processcomprising: passing a preheated process gas through said reformingsection, heating the at least one catalyst tube in the reforming sectionby indirect heat exchange with a gas-liquid mixture that self-circulatesand is encapsulated inside a common volume containing said reformingsection and said boiler section, retrieving reformed process gas fromsaid reforming section and optionally cooling said reformed process gasby preheating of the feed process fluid, introducing a fuel into the atleast one burner in the combustion section together with combustion air,in which said combustion air is preheated by indirect heat exchange withflue gas from the boiler section, retrieving flue gas from the burnerand passing said flue gas through a boiler section, and heating saidgas-liquid mixture that self-circulates and is encapsulated inside acommon volume in the reactor containing said reforming section and saidboiler section by indirect heat exchange with the flue gas passingthrough said boiler section.